**5. General conclusions**

Nowadays, an excessive use of fossil fuels has led to significant emissions of CO2 in the atmosphere which is responsible for causing extensive climate changes (Soccol et al., 2010). As a result of this with the increase in fossil fuel prices direct the efforts towards utilizing renewable energy sources. Considerable progress in searching for alternative energy sources has been made since the oil crisis of 1973. However, it must be noted that an only the renewable biomass used for energy production contributes to the reduction of negative environmental impacts, e.g. decreased GHG emissions.

Currently, commercial biofuels production, such as ethanol and biogas, relies mostly on the fermentation of cane sugar, molasses or glucose derived from corn, sugar beet, wheat or potatoes. It is not economically accepted because these biomass production for biofuels competes for the limited agricultural land needed for food and feed production. Much of the hydrogen produced in the world is obtained from natural gas, which is not environmental friendly. Therefore, a significant increase in biofuels production would be possible only if technologies are developed to convert the waste biomass.

Dairy industry, like most other food industries, generates strong wastewaters characterized by high COD concentrations representing their high organic content (Demirel et al., 2005). Whey is by-product of milk processing and is abundantly obtained during cheese production. According to Najafpour et al. (2008), worldwide cheese production generates more than 145 million tonnes of liquid whey per year. In the case of deproteination of whey for the production of a valuable human food additive, the residual whey permeate is still a waste with high COD and must be treated before disposal. Due to its lactose major component, whey permeate is a well defined and suitable substrate for anaerobic digestion (Kourkoutas et al., 2002; Najafpour et al., 2008; Venetsaneas et al., 2009; Zafar & Owais, 2006). UF whey permeate fermentation in UASB reactors to produce biofuels (bioethanol, biogas, biohydrogen) has been successfully tested in this study.
